Just thought I'd add a bit more re preload. Just had a ride for a few hours this afternoon and an hour in the hot tub so the mind is now clear!
Preload also changes ride height, so more at the front will raise it and slow the steering a little and add a little stability. This can be compensated for by raising or lowering the forks in the triple clamps
It is extremely important to get the sags correct and preload is a tool to assist in that. Can't remember what the book says, but if you know the travel, for dirt bikes, look for about 10% of travel taken up by the weight of the bike alone. Then when you sit on board with all gear look for about 1/3 of travel to be used up, front and rear.
If you use lots of preload to get the laden sag set then you will struggle to get the unladen sag right. This means that you need a heavier spring, and visa versa. In this scenario this will also improve the compliance, ie smooth the ride with a heavier spring. Imagine for example that you had 0.44 fork springs. This means that for every mm of travel in the forks they need to have 0.88 kg applied. If you add 10 mm of preload then you need to apply 8.8 kg before the springs will move again. So a heavier spring with less preload will offer better compliance and better bottoming resistance.
Steve
